Beginning in April 2018, Medicare beneficiaries will begin receiving replacement Medicare ID Cards that no not have their Social Numbers numbers as part of their ID number. The new ID number will be 11 characters long and will include both letters and numbers. This new ID will be known as the Medicare Beneficiary Identifier (MBI) and will be confidential like the Social Security number. The change is intended to fight identity theft targeted at the 57 million senior Americans on Medicare.